SCAD ENGINEERING COLLEGE, SERANMAHADEVI

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

QUESTION BANK

SUB: CIRCUIT THEORY FACULTY NAME: T.RAMACHANDRAN

SUB CODE: EE6201 SEM/BRANCH: II/ EEE AND ECE

2 marks and 16 marks

Unit-I

1. State the limitation of ohm’s law. (May/June 2013)*2. Distinguish between mesh and loop of an electric circuit. (May/June 2013)3. How are the following affected by change of frequency (May/June 2012)

a. Resistance b. inductive reactance4. Define nodal analysis of a circuit. (May/June 2012)5. A bulb is rated as 230V, 230W. Find the rated current and

resistance of the filament. (April/May 2011)6. Define mesh analysis of a circuit. (April/May 2011)7. Two coils, connected in parallel across 100V dc supply mains, take 10 A from mains. The power

dissipated in one coil is 600W. What is the resistance of each coil? (April/May 2011)8. State ohm’s law and give its limitations. (April/May 2011)9. List the active and passive elements of electric circuit. (May/June 2011) 10. Write any two different between series and parallel circuits. (May/June 2011)11. Give example for voltage source and current source. (May/June 2011)12. 3 fans are connected in parallel across 200V. each is rated at 100W,110W,120W respectively.

How much current flow through each and what is the total current? (June/July 2010)13. Two resistance 8 ohm and 10 ohm are connected in parallel. A resistor of 12 ohm is connected

in series with this combination; a voltage of 200V is applied across the entire circuit. Find the current in each resistor and voltage across the 12 ohm resistor. (June/July 2010)

14. A resistor R is connected in series with parallel circuit comprising two resistors of 12 ohm and 8 ohm. The total power dissipated in the circuit is 700W, when the applied voltage is 200V. calculate the value of R. (June/July 2010)

15. Two circuits A & B are connected in parallel across 200V, 50Hz supply. Circuit A consists of 10 ohm resistance and 0.12H inductance in series while circuit B consists of 20 ohm resistance in series with 40 micro F capacitance. Calculate current in each branch. (June/July 2010)

16. State Kirchhoff’s voltage law. (May/June 2010)17. Difference between series and parallel circuit. (June/July 2010)18. A voltage divider circuit of two resistances is designed with a total resistance of the two resistors

equal to 50 ohm. If the out put voltage is 10% of the input voltage, obtain the values of the two resistors in the circuit. (June/July 2009)

19. A 25 ohm resistance has a voltage v= 150 sin377t Volta. Find the corresponding current and power. (June/July 2010)

20. Two capacitors C1 and C2 are connected in series and the value of C1 is 10 micro F and the equivalent capacitance is 1.67 micro F. find the C2 (June/July 2010)

21. State and explain Kirchoffs laws (6) (May/June 2013)

22. Using mesh analysis, determine the current through 6V source in the circuit shown in fig (10) (May/June 2013)

23. Three loads A, B and C are connected in parallel to a 240V source. Load A takes 9.6KW, load B takes 60A and load C has a resistance of 4.8Ω. calculate (i) Ra and Rb (ii) the total current (iii) the total power, and (iv) equivalent resistance (6) (May/June 2013)

24. By applying nodal analysis for the circuit shown below (i) determine the current in each branch(ii) power in each resistor (10) (May/June 2013)

25. The value of Vr and Vl were measured and found to be 10 V each. Determine the frequency and i(t). and the value of total impedance and e(t). (6+4) (May/June 2012)

Unit-II

1. State the voltage division principle for two resistors in series and the current division principle for two resistors in parallel. (May/June 2013)

2. State maximum power transfer theorem. (May/June 2013)3. Find the equivalent current source for a voltage source of 100V with a series resistance of 2 Ω.

(May/June 2012)4. State reciprocity theorem. (May/June 2012) (May/June 2011)5. Transform the circuit shown below, from ∆ to Y. (April/May 2011)6. Two resistors connected in series have a resistance of 18 ohms and

when connected in parallel and have a resistance of 4.5 ohms when in parallel. Find the value of resistance. (April/May 2011)

7. Three resistors A,B and C are connected in series to a 240V supply. If Ra=60 ohms and Eb=40V when the current in the circuit is 0.5A. Calculate Rb and Rc. (April/May 2011)

8. A delta network consists of equal resistances in all the three arms. Find the resistance of the arms of its equivalent star. (April/May 2011)

9. Obtain the equation for the current through two resistors when they are in parallel using current division rule. (April/May 2011)

10. State thevenin’s theorem. (April/May 2011)11. Define current division rule. (May/June 2011)12. Find the equivalent current source for the circuit shown below. (June 2010)13. What is the limitation of superposition theorem? (June/July 2010)14. State maximum power transfer theorem in a dc circuit. (June 2010)*15. Write the expression for star to delta transformation. (June 2010)16. State norton’s theorem. (June/July 2010)17. Give condition for maximum power transfer in DC and AC circuit. (June/July 2010)18. Find the thevenin’s equivalent for the circuit shown below. (June/July 2010)19. Calculate the current through 50 ohm and 10 ohm resistor in the below circuit. (June/July 2009)20. Explain the source transformation technique(6) (May/June 2013)21. Use superposition theorem to find the current through 4Ω resistor in the circuit shown in below

fig (10) (May/June 2013)

22. Derive expression for star connected resistance in terms of delta connected resistance(8) (May/June 2013)

23. Find current through branch 6 ohm of the network shown in below fig using thevenin’s theorem(8) (May/June 2013)

24. Use the technique of delta –star conversion to find the equivalent resistance between terminals A-B of the below circuit. (8) (April/ May 2011)

Unit-III

1. Define band width of a resonance circuit. (May/June 2013)2. Give the application of tuned circuits. (May/June 2013)3. Define resonance network. (May/June 2012)4. State dot rule for coupled circuits. (May/June 2012)5. When do you say that a circuit is in resonance?6. Two inductively coupled coils have self inductance L1=50 mH and L2= 200 mH. If the coefficient

of the coupling is 0.5, compute the value of mutual inductance between the coils. (April/May 2011)

7. Obtain the resonance frequency of a series RLC circuit. (April/May 2011)8. A series RLC circuit with Q=250 is resonant at 1.5 MHz. find the frequencies at half power points

and bandwidth. (April/May 2011)9. Define the co-efficient of coupling. (April/May 2011)*10. Two coupled coils of L1=0.9 H and L2 H have a coupling co-efficient K 0.8. Find the mutual

inductances M and turns ration N2/N1. (April/May 2011)11. What are coupled coil. (May/June 2011)12. Define mutual inductance. (May/June 2011)13. Find the Q factor of the RLC series circuit which has R=50 Ω, L=50 mH and C= 1800pF.

(May/June 2011)14. Two magnetically coupled coils have self inductance L1= 100mH, L2=400mH and mutual

inductance M=160 mH. Find the coefficient of coupling. (May/June 2011)15. In a series RLC circuit , if the value of L and C are 100 µH and 0.1µF respectively, find the

resonance frequency in Hz (June 2010)16. In a coupled circuit having two coils, the value of L1,L2 and K are are 5 mH, 10mH and 0.8

respectively where K is coefficient of coupling. Find the mutual inductance between the two coils. (June 2010)

17. Write the relationship between quality factor and bandwidth. (June 2010)18. If K be the coefficient of coupling between two inductors of inductance of L1 and L2 connected

in parallel, write the expression for total inductance. (June 2010)19. A series RLC circuit has the following parameters that R=10 ohm, L=0.01 H ,C= 100 micro F.

calculate the resonance frequency, quality factor of the circuit, bandwidth , lower and upper frequency of bandwidth. (June/July 2010)

20. Two inductively coupled coils have self inductance L1=45 mH and L2=150 mH. If the coefficient of the coupling is 0.5. (i) find the value of mutual inductance between the coils. (June/July 2010)

21. Compare series resonance and parallel resonance. (June/July 2010)22. Mention some uses of tuned circuits. (June/July 2010)23. Define self inductance. (June/July 2010)24. Write the condition for resonance in series RLC circuit. (June/July 2009)25. Derive the resonance frequency f for the circuit in below fig(8) (May/June 2013)26. A series circuit with R = 10Ω, l = 0.1 H and C = 50µF has an applied voltage V = 50L0 V with a

variable frequency. Find (i) the resonant frequency (ii) the value of frequency at which maximum voltage occurs across inductor (iii) the value of frequency at which maximum voltage occurs across capacitor and (iv) the quality factor of the coil. (8) (May/June 2013)

27. Derive the expression for the coefficient of coupling in terms of mutual and self inductances of the coils (8) (May/June 2013)*

28. The (Rl+j20) Ω and (20-j10) Ω are connected in parallel determine the value of Rl for resonance. (6) (May/June 2012)

29. Derive the relationship between self inductance, mutual inductance and coefficient of coupling. (8) (May/June 2012)

30. Find the resonance frequency for the below shown circuit. (10) (April/ May 2011)

31. Determine the quality factor of a coil for the series circuit consisting of R=10 ohm, L=0.1 H and C=10 micro F. derive the formula used. (6) (April/ May 2011)

32. Derive the expression for maximum out put voltage and maximum amplification of a single tuned circuit. (8) (April/ May 2011)

33. A series RLC circuit with R=10 ohms, L=10 mH and C=1 micro Fhas an applied voltage of 200V at resonance frequency. Find the resonance frequency, the current in the circuit and voltage across elements at resonance. Find also quality factor and bandwidth. (12) (April/ May 2011)

34. A series RLC circuit has an impedance of 40 ohmat a frequency of 200 radians/seconds. When the circuit excited by a 10 V source of frequency, the circuit resonate at a frequency of 250 radians/seconds. The current at resonance is 0.5 A and the quality factor at resonance is 10. Determine the circuit parameters.(6) (April/ May 2011)

35. A coil of inductance of 31.8 mH and resistance of 10 ohm is connected in parallel with a capacitor across a250V, 50 Hz supply. Determine the value of capacitance if no reactive current is taken from the main suply.(6) (April/ May 2011)

36. Two coils connected in series have an equvalent resistance of 0.8 H when connected in adding and an equivalent inductance of 0.4 H when connected in apposing. Determine the mutual inductance. Calculate the self inductance of the coils, by taking K=0.55. (6) (April/ May 2011)

Unit-IV

1. Find the time constant of RL circuit having R=10 Ω and L=0.1 mH. (May/June 2013)2. A RLC series circuit has R=10 Ω L= 2H. What value of capacitance will make the circuit critically

damped? (May/June 2013)3. Sketch the transient current i(t) vs t graph for a series RL circuit. (May/June 2012)4. Consider two cases RC parallel circuit shown below. First case DC voltage is applied and second

case AC voltage is applied. Compare how the capacitor gets charged in the two cases. (May/June 2012)

5. Define a tern time constant of a circuit in general. (April/May 2011)6. A coil having a resistance of 10 K Ω and inductance of 50 mH is connected to a 10 V 10KHz

power supply. Calculate the impedance.7. Why transient occur in electric circuit.8. Define the time constant of RC circuit.9. What is the time constant of RL circuit with R=10 Ω and L=20 mH.10. A series RL circuit with R=10 Ω is excited by a dc voltage of 30 V by closing the switch t=0.

Determine the current in the circuit at twice the time constant. (April/May 2011)11. Write the expression for the critical resistance and damping ratio of RLC series circuit.

(May/June 2011)12. In a RC series circuit with R=10 K Ω and C= 40μF. Find the time constant. (May/June 2011)13. Draw the capacitor charging current in a RC series circuit with DC source. (May/June 2011)14. A series RL circuit with R =100Ω and L = 20 H has a DC voltage of 200V applied through a switch

at t =0. Assume the initial current through the inductor t= 0 is zero, find the current at t=0.5 sec. (June 2010)

15. What is the condition to be present in a series RLC circuit to make the circuit critically damped? (June 2010)

16. Define steady state response of a system. (June 2010)17. Write a note on transient response. (June/July 2010)18. Define time constant of a transient response (June/July 2009)

19. Derive the step response of the RL and RC circuits. Compare their performances (16) (May/June 2013)

20. Derive an expression for the current response of RLC series circuit with sinusoidal excitation. Assume that the circuit is working in critical (16) (May/June 2013)

21. Derive the transient response of RLC series circuit with DC input, using Laplace transform.(16) (May/June 2012)

22. A series RLC circuit with R=3000 ohm, L=10 H and C=200 micro F has a Constance voltage of 50 Applied at t=0. Find the current transient and the maximum value of the current assuming the initial conditions zero. (6) (April/ May 2011)

23. In the series RLC circuit, the applied voltage at t=0 is e=100e-50t. Find the resulting current and the initial rate of change of current. Take R=50 ohm and L=20 mH. (6) (April/ May 2011)

Unit-V

1. What is phase sequence of a 3 phase system? (May/June 2013)2. A delta connected load has (30-j40) Ω impedance per phase. Determine the phase current if it is

connected to a 415V, 3 phase, 50 Hz supply. (May/June 2013)3. Define power factor of a circuit. (May/June 2012)4. A 3 phase 440V supply is given to a balanced star connected load of impedance (6-j8) in each

branch. Find the magnitude of the line current. (May/June 2012)5. In a 3 phase balanced delta system, the voltage across R and Y is 400L0 V. What will be the

voltage across Y and B? Assume RYB phase sequence. (April/May 2011)6. Calculate the power factor if v(t)=Vm sin wt and i(t)= Im sin (wt-45)? (April/May 2011)7. A star connected load has 6+ j8 Ω impedance / phase. Determine the current if it is connected to

400 V, 3 phase 50 Hz. (April/May 2011)8. What is phase sequence? (April/May 2011)9. A balanced star connected load of 4-j6 Ω impedance is connected to 400V 3 phase supply. What

is the power and power factor?10. Write the expression for the power factor in two watt meter method of power measurement.

(April/May 2011)11. A balanced star connected load having the voltage across the terminals R and Y is 400V.

Calculate the values of the three line voltages. Assume RYB phase sequence. (April/May 2011)12. Write any two differences between current coil and voltage coil of a wattmeter. (May/June

2011)13. What is the power factor if the two wattmeter’s connected to measure three phase power read

1000W each, both positive. (May/June 2011)14. What is mean by balanced load in a 3 phase system? (June 2010)15. Define power factor. (June 2010)16. A balanced star connected load of (3-j4) ohm impedance is connected to 400V 3 phase supply,

what is the real power consumed by the load? (June/July 2010)17. Write the expression for the power factor in a balanced three phase circuit. (June/July 2010)18. A 3 phase balanced wye connected load has 400V line to line voltage and 10A line current.

Determine the line to neutral voltage and phase current. (June/July 2010).19. Mention some advantages of 3 phase system over 1 phase system. (June/July 2010)20. Compare balanced and unbalanced network. (June/July 2009)21. A three phase balanced load has 500V line to line voltage and 10A line current. Determine the

phase voltage and phase current. (June/July 2009)22. Draw the phasor diagram of phase and line voltages and currents in a delta connected balanced

load. (June/July 2009)23. What are the advantages of the 3 phase system (4) (May/June 2013)

24. Prove that the total instantaneous power in a balanced 3 phase system is equal to the average power whether the load is star or delta connected (10) (May/June 2013)

25. The two wattmeter method produces wattmeter readings, readings P1= 1560 W and P2= 2100 W when connected to a delta connected load. If the line voltage is 220. calculate (i) the per phase average power (ii) the per phase reactive power (iii) the reactive power and (iv) the phaseimpedance (12) (May/June 2013)

26. A 3 phases balanced delta connected load of (4+j8) is connected across a 400V, 3 phase supply. Determine the phase currents and line currents. Assume the RYB phase sequence. Also calculate the power drawn by the load. (8) (May/June 2012)

27. Three equal inductors are connected in star; take 5 KW at 0.7 pf when connected to a 400V, 50Hz, three phase three wire supply. Calculate the line current(i) if one of the inductor is disconnected and (ii) if one of the inductor is short circuited .(8) (May/June 2012)

28. If W1 and W2 are the readings of two wattmeters which measure the power in the three phase balanced system and if W1/W2 = a, show that the power factor of the circuit is given by Cos φ = a+1/ a2-a+1 (8) (May/June 2012)

29. Obtain the readings of two wattmeters connected to a three phase 3 wire system 120V feeding a balanced delta connected load with a load impedance of 12L30 W. assume either phase sequence . Find the phase power and compare the total power to the sum of wattmeter readings.. (8) (May/June 2012)

30. A balanced four wire star connected load has balanced supply voltage of 400V. the load impedance of Zr=4+j8 ohm, Zy=3+j4 ohm and Zb= 15+j20 ohm. Calculate the line currents and neutral current. (8) (April/ May 2011)

31. Each of two wattmeters connected to measure the power input to a 3 phase circuit read 10 KW on a balanced load, when the power factor is unity. What the instrument read when the power factor falls to 0.866 lagging. (4) (April/ May 2011)